Hot water is an essential commodity in the modern world, and a water heating system is an appliance commonly used in households throughout the world.
In some countries where the price of the energy is negligible, it is common to activate the water heating system all the day, resulting in a significant waste of energy.
In other countries, where energy is relatively expensive, solar energy is used for heating the water. However, the solar energy cannot generally provide hot water 24 hours a day, 365 days a year, and therefore complementary heating involving energy consumption is required. The source of energy for this purpose is, in most cases, electricity or gas.
In order to save energy, activation of the water heating is only as needed. However, in most water heating systems of the prior art, the user is not provided with any indication regarding temperature of the water in the tank, and moreover, he has no indication whatsoever regarding how long the heating system has to be ON in order to provide water in the desired amount and temperature. Generally, this causes the user to activate the heating element of the system a longer time than necessary resulting in a waste of energy, or a shorter time than necessary, resulting in a colder and insufficient amount of water than desired. Furthermore, even after the water heating is presumably completed, the user has no indication of the water temperature in the tank, and must open the tap and wait a relatively long time for regulating the temperature, resulting in a waste of water.
The lack of accurate temperature indication of the water in the tank, and the inability to plan in advance the necessary water amount and temperature causes inconvenience, waste of energy and water. In cases wherein the user constantly activates the water heating throughout the day and night, there is even more energy waste, particularly in times when there is no need for hot water. This energy waste is added to the energy loss resulting from the temperature difference between environment and the water in the tank, which in many cases is significant.
Of course there are times where a user requires a relatively hotter temperature than in other times. In the systems of the prior art, the pre-planning of the water temperature is either unavailable, or unsatisfactory. In conventional water heating systems of the prior art, and particularly for safety purposes, there is an adjustable thermostat mounted in a pocket in the water tank, which senses the water temperature, and disconnects the electrical supply when a pre-assigned maximum temperature is reached. However, in this case, the regular user does not have access to the thermostat, or control over the pre-assigned temperature.
Some other prior art systems comprise a timer, either electrical or mechanical, for setting the duration of the water heating.
FIG. 1 shows a hot water tank 1 commonly used in systems of the prior art. The water tank 1 comprises an electric heating unit 3 for supplying energy to the water. Heating unit 3 is essentially a resistor, heated by an electric current flowing through it, and transferring heat to the surrounding water. The water tank further comprises in its lower part an inlet water pipe 8, and in its upper part an outlet water pipe 9. Two optional water pipes 104 and 105 are included in those standard water tanks that are designed to operate with solar heat collectors. Through pipe 105 cold water leave the tank to a solar collector, and through pipe 104 hot water enter the tank from the solar collector (not shown). Metal flange 2 at the bottom of the tank supports the heating unit 3. Also supported by the flange is a metal sleeve 4, serving as a pocket for a standard thermostat. Insulating layer 5 blocks heat transfer to the surroundings. Thin metal 10 encloses the tank and the insulating layer 5. Remote ON/OFF switch 6, is usually located in an easily accessed place, and generally comprises a red indication that lights up when the switch is ON. When the switch is ON and the water temperature rises to the preset temperature of the thermostat, the thermostat disconnects current to unit 3. When the water temperature falls below said preset temperature, the thermostat reconnects the current to the heating element.
FIG. 1 also shows a prior art system that further comprises a heat concentrator 7 in the water tank. The heat concentrator 7, which is used only in a vertically oriented tank, is a cup-like device made of any suitable material, mechanically connected to the bottom of the water tank. The heat concentrator 7 has openings 19 at its lower part for enabling water passage into it, and at its upper part an additional outlet opening 20. The heat concentrator 7 encloses the heating unit 3 and the thermostat pocket 4. When the heating unit 3 is activated, hot water in concentrator 7 flows to the upper opening 20, and cold water flows through the lower openings 19 to the concentrator, creating water circulation. Layers of hot water are therefore concentrated at the upper part of the water tank. After a long period of heating, all the water in the tank becomes sufficiently hot, and the water temperature in different parts of the tank is relatively homogeneous.
Generally, it is common to use a heat concentrator 7 in water tanks of 80 liters or more.
Prior art
U.S. Pat. No. 6,002,114, filed Sep. 15, 1998, discloses a water heating system which comprises:    1. A water tank with four heating elements;    2. Temperature sensors for checking the temperature at the inlet and outlet of the water tank;    3. A sensor for checking the water flow rate at the inlet pipe of the tank;    4. CPU receiving sensor indications, for activating/deactivating said four heating elements, further comprising a circuitry for detecting failures; and    5. A display panel for showing the user the temperature of the water leaving the tank.
More particularly, U.S. Pat. No. 6,002,114 deals with a commercial heating system having four electric heating elements, and a plurality of sensors. The heating elements are activated according to water temperature at the inlet and outlet of the tank, while further considering the inlet water flow rate.
DE 29719 267 discloses a microprocessor-based controller for an electric water heating system. The front panel of the housing of the controller has several push buttons for setting the desired temperature and various other parameters, for selecting from a function menu, and for activating a rapid heating mode. The controller further comprises a seven-segment display with a temperature bar indicating the thermal state of the heating system.
U.S. Pat. No. 5,556,564 discloses a domestic water heating system having a unit for controlling the water temperature. The said system comprises:    1. Three temperature sensors, a first sensor at the top, next to the outlet of the water from the tank a second in the middle of the tank, and a third at the bottom of the tank next to the water inlet;    2. A display panel showing the temperature measured by the upper sensor, and enabling the user to set the required temperature of water leaving the tank;    3. Two light indicators which deactivate when the middle, and the lower sensors measure temperatures above the set temperature. The light indicators indicate to the user when there is enough water in the tank for use.    4. The hot water tank and the control panel are distant one from the other, and are connected by only two electric wires. The same two electric wires provide the power to the heating element, and transfer the low voltage temperature indication from the upper sensor in the tank to the control panel.
FR 2 539 238 discloses a control method and device for an apparatus for heating a fluid to reach a predetermined temperature. The device comprises a central control unit receiving a signal from a temperature probe which identifies the temperature of the fluid, a storage unit for storing a characteristics data of the apparatus used, and a circuit for setting a predetermined temperature. The invention is particularly useful in electric water heating systems. The system of this patent particularly intends to activate the heating doing low-rate electrical periods, for example, overnight, weekends, etc. This patent identifies the periods of low-cost electric energy in order to activate the heating particularly during these periods. The system follows the expressions: th=(TF′−TD); and 1<K+ta. th is the temperature at the end of the low cost electric energy period. TF′ is the time at the end of the low cost electric energy, TD is the present time, K is a factor describing the intensity of the electric power at the heating element and the water volume in the tank. This formula cannot determine the time required for heating the water in the tank. All this is available for one cycle a day. The system also enables manual heat activation for times when the energy cost is higher.
U.S. Pat. No. 4,568,821 discloses still another remote water heating system. The system comprises two water tanks, one tank solar heated, the other heated by electricity, oil or gas. The system comprises two temperature sensors located at the outlet pipes of each water tank. The controller of said system uses a 24-hour clock, and is assembled with solid state electronic components.
All the above prior art systems are designed to provide better control over water heating systems, and to save energy. Some of the prior art systems allow the designating of a period for heating with a starting time. However, these systems do not consider the water temperature at the starting time for heating, in which the water is heated for the said designated period, resulting in hotter water than necessary (and waste of energy) or colder than necessary (resulting in inconvenience). In some other cases, the water reaches the desired temperature before the time planned for use, and the heating terminates. However, until the water is actually used, the temperature decreases, resulting in a waste of energy and inconvenience. The water heating system of the invention provides more energy and water saving in comparison with the prior art water heating systems, a manner for efficient installation, and also more convenience for the hot water user.
The present invention also discloses a new, efficient and easy manner of assembling temperature sensing units in a water tank, as required by the system of the invention, therefore obtaining more accurate temperature sensing, and improving even more the energy and water saving. Such a manner of assembling the system of the invention is applicable in both existing water heating systems or in newly installed water heating systems
It is therefore an object of the invention to increase energy and water savings in a domestic water heating system.
It is another object of the invention to provide to the user better control and more reliable indications relating to the temperature of the water in the tank.
It is still another object of the invention to enable easy installation of the system of the invention, in existing water heating systems, on site.
It is still another object of the invention to provide electrical and electronic failure indications, by visual or audible means.
It is still another object of the invention to provide an easy manner of installation of the system of the invention in new or existing water heating systems. This manner of assembling relates particularly to the introduction and assembling of temperature sensing units in the tank.
It is still another object of the invention to provide new manner by which data is communicated between the temperature sensing unit/s of the tank generally located outside of the house, and the control unit located inside.